Stress metabolisms induced by severe trauma, large abdominal surgery procedures, sepsis, etc. leads to metabolic changes, which increase energy expenditure, enhanced protein catabolism, insulin resistance. Muscle proteolysis is massively stimulated. Critically ill patients pay for survival with a loss of muscles. Enteral nutrition, especially protein delivery to critically ill, is very important for optimizing their outcome. Standard enteral feeding regiments are generally based on continuous feeding, which is thought to be better tolerated by critically ill patients with easier glycaemic control by continuous infusion of insulin, translated in less glycaemic variability. But this approach is not physiological, continuous feeding does not allow protein synthesis. Optimal protein synthesis requires a pulsatile increase in branched-chain amino acids. Bolus feeding activates the entrohormonal axis (bioactive peptides, insulin), and stimulates skeletal muscle synthesis to the maximum extent. The question is, whether bolus enteral feeding in critically ill patients with limited gastrointestinal function delivers a greater amount of protein, improves nutritional parameters, with higher quadriceps muscle layer thickness (QMLT) and muscle strength.

The trial has been designed in accordance with the Recommendations for Interventional Trials (SPIRIT 2013) and the Consolidated Standards for Reporting of Trials CONSORT guidelines.

Patients who meet the study inclusion criteria (severe trauma patients, surgical patients and medical patients with sepsis, with inserted nasogastric/nasoduodenal feed-ing tube) will be eligible to participate, especially patients who are mechanically ventilated. The last criterion is not a necessary precondition (a module of indirect calorimetry will be used in these patients). The necessary condition is the elimination of shock within 24 hours from the ICU admission and tolerance of trophic enteral feed-ing (20ml/hour) at for the period of at least 24 hours. Patients will be randomized in a ratio of 1:1 within 72 hours of their admission to receive bolus or continuous enteral feeding (sealed envelopes method). In both groups, the same goals of energy and protein will be observed (Day 1-2: E 15 kcal/kg/day, protein 0.8-1 g/kg/day; Day 3-4: E 20 kcal/kg/day, protein 1. 2 g/kg/day; Day ≥ 5: E 25 kcal/kg/day, protein 1.5-2 g/kg/day), according to protocol. The bolus enteral group will receive the amount of enteral nutrition in six boluses (per 60min dose), the continuous enteral group will receive the amount using a pump, within the timeframe of 6am-24pm. The need for parenteral nutrition will be determined by treating clinical staff independently to group allocation.

Demographic data collection: (weight, high, BMI) and conditions (trauma, surgical, medical patients), Acute Physiology and Chronic Health Evaluation (APACHE) Sequential Organ Failure Assessment (SOFA), Nutritional Risk Screening (NRS 2002).

Daily observations: glucose, mean glucose changes, insulin (IU/d), energy and protein intake (administered calories divided by the calculated energy expenditure and administered protein divided by calculated protein intake) - Adjusted/calculated energy and protein (%). Feeding intolerance (tolerating less than 40% of requirements via the enteral route for ≥ 3 days, diarrhea ≥ 500ml per day or five bowel actions). Mechanically ventilated patients (Resting Energy Expenditure (REE) and Respiratory Quotient (RQ) measured with indirect calorimetry) Day 1, 3, 5, 7: Nutritional parameters (serum albumin prealbumin, C-reactive protein (CRP), urine urea, N balance).

Day 1 and 7: Muscle layer thickness (QMLT by ultrasound measurement and mid-upper arm circumference) and muscle strength (dynamometer) from baseline to discharge. Outcomes of muscle strength/ultrasound and dynamometer) will be measured by an investigator blinded to the group allocation.

Inclusion Criteria:

• polytrauma
• major abdominal surgery
• sepsis
• ICU stay
• enteral feeding tube
• artificial ventilation

Exclusion Criteria:

• contraindication of enteral feeding
• infaust prognosis
• prolonged shock (more than 24 hours)

There is no plan to make individual participant data available to other researchers.

No masking will be used in the study.